Systematic Testing Skill

Purpose

Guide test-driven development (TDD), generate comprehensive test suites, and provide systematic debugging frameworks. Ensures code is well-tested and bugs are resolved methodically rather than through trial-and-error.

Activation Triggers

Activate this skill when:

User implements new functionality (auto-suggest tests)
Tests fail (activate debugging framework)
User says "write tests for this"
User mentions "TDD" or "test-driven"
User asks about debugging or troubleshooting
User says "this bug..." or "error..."
Before marking feature complete (verify test coverage)

Core Capabilities

1. Test-Driven Development (TDD)

For complete TDD workflow, use Skill tool to invoke: dev-workflow:test-driven-development

How to activate:

Use Skill tool: Skill(skill: "dev-workflow:test-driven-development")

The test-driven-development skill provides:

Full RED-GREEN-REFACTOR cycle explanation
Strict TDD enforcement and discipline
Anti-patterns and rationalizations to avoid
Detailed examples and verification checklist

Quick TDD Summary:

RED: Write failing test first
GREEN: Write minimal code to pass
REFACTOR: Clean up while tests stay green

This skill focuses on test generation strategies and systematic debugging. For TDD methodology details, use the dedicated skill.

2. Test Generation

Goal: Generate comprehensive test suites covering all scenarios

Test Categories

Normal Cases (Happy Path)

Test expected, typical usage:

describe('calculatePositionSize', () => {
  it('should calculate correct position size for valid inputs', () => {
    const result = calculatePositionSize(
      10000,  // account balance
      0.02,   // 2% risk
      150.50, // entry price
      148.00  // stop loss
    );

    expect(result).toBe(80); // $200 risk / $2.50 per share
  });

  it('should handle large account balances', () => {
    const result = calculatePositionSize(
      1000000, // $1M account
      0.01,    // 1% risk
      100,
      99
    );

    expect(result).toBe(10000);
  });
});

Edge Cases (Boundary Conditions)

Test limits and boundaries:

describe('calculatePositionSize - edge cases', () => {
  it('should handle very small risk percentage', () => {
    const result = calculatePositionSize(
      10000,
      0.001, // 0.1% risk
      100,
      99
    );

    expect(result).toBe(10); // $10 risk / $1 per share
  });

  it('should handle entry price equal to stop loss', () => {
    expect(() => {
      calculatePositionSize(10000, 0.02, 100, 100);
    }).toThrow('Entry price cannot equal stop loss');
  });

  it('should handle very small price differences', () => {
    const result = calculatePositionSize(
      10000,
      0.02,
      100.10,
      100.00
    );

    expect(result).toBe(2000); // $200 / $0.10
  });

  it('should round down fractional shares', () => {
    const result = calculatePositionSize(
      10000,
      0.02,
      150.75, // Creates fractional result
      148.00
    );

    // Should be whole number, not fractional
    expect(Number.isInteger(result)).toBe(true);
  });
});

Error Cases (Invalid Inputs)

Test error handling:

describe('calculatePositionSize - error cases', () => {
  it('should reject negative account balance', () => {
    expect(() => {
      calculatePositionSize(-10000, 0.02, 100, 99);
    }).toThrow('Account balance must be positive');
  });

  it('should reject zero account balance', () => {
    expect(() => {
      calculatePositionSize(0, 0.02, 100, 99);
    }).toThrow('Account balance must be positive');
  });

  it('should reject risk percentage over 100%', () => {
    expect(() => {
      calculatePositionSize(10000, 1.5, 100, 99);
    }).toThrow('Risk percentage must be between 0 and 1');
  });

  it('should reject negative risk percentage', () => {
    expect(() => {
      calculatePositionSize(10000, -0.02, 100, 99);
    }).toThrow('Risk percentage must be between 0 and 1');
  });

  it('should handle null inputs gracefully', () => {
    expect(() => {
      calculatePositionSize(null, 0.02, 100, 99);
    }).toThrow();
  });

  it('should handle undefined inputs gracefully', () => {
    expect(() => {
      calculatePositionSize(undefined, 0.02, 100, 99);
    }).toThrow();
  });
});

Integration Cases

Test component interactions:

describe('login flow - integration', () => {
  it('should complete full authentication flow', async () => {
    // Test entire flow from request to response
    const response = await request(app)
      .post('/api/auth/login')
      .send({
        email: 'user@example.com',
        password: 'SecureP@ss123'
      });

    // Verify response
    expect(response.status).toBe(200);
    expect(response.body.data.accessToken).toBeTruthy();

    // Verify token is valid
    const decoded = jwt.verify(
      response.body.data.accessToken,
      process.env.JWT_SECRET
    );
    expect(decoded.id).toBeTruthy();

    // Verify user can access protected route
    const protectedResponse = await request(app)
      .get('/api/user/profile')
      .set('Authorization', `Bearer ${response.body.data.accessToken}`);

    expect(protectedResponse.status).toBe(200);
  });

  it('should prevent access with expired token', async () => {
    // Create expired token
    const expiredToken = jwt.sign(
      { id: 'user-id' },
      process.env.JWT_SECRET,
      { expiresIn: '-1h' } // Already expired
    );

    // Attempt to access protected route
    const response = await request(app)
      .get('/api/user/profile')
      .set('Authorization', `Bearer ${expiredToken}`);

    expect(response.status).toBe(401);
    expect(response.body.error.code).toBe('TOKEN_EXPIRED');
  });
});

Test Generation Template

describe('[Component/Function Name]', () => {
  // Setup and teardown
  beforeEach(() => {
    // Reset state, create test data
  });

  afterEach(() => {
    // Clean up, reset mocks
  });

  // NORMAL CASES
  describe('normal operation', () => {
    it('should [expected behavior for typical input]', () => {
      // Test implementation
    });
  });

  // EDGE CASES
  describe('edge cases', () => {
    it('should handle [boundary condition]', () => {
      // Test implementation
    });
  });

  // ERROR CASES
  describe('error handling', () => {
    it('should reject [invalid input]', () => {
      expect(() => {
        // Call with invalid input
      }).toThrow('Expected error message');
    });
  });

  // INTEGRATION
  describe('integration', () => {
    it('should work with [other component]', () => {
      // Test interaction
    });
  });
});

3. Systematic Debugging Framework

Goal: Resolve bugs methodically, not through random trial-and-error

Four-Phase Framework:

Phase 1: Root Cause Investigation

Goal: Understand exactly what's going wrong

Process:

Reproduce Bug Consistently

Steps to reproduce:
1. Navigate to login page
2. Enter email: user@example.com
3. Enter password: TestPass123
4. Click submit
5. Observe: Error message "Network request failed"

Reproducibility: 10/10 attempts failed

Identify Symptoms
- What's the visible error?
- What error messages appear?
- What's the expected vs actual behavior?

Gather Evidence

# Check logs
tail -f logs/app.log

# Check network requests (browser dev tools)
# Check console errors
# Check server logs

Collect:

Error messages (full text)
Stack traces
Log entries
Network requests/responses
Input values that trigger bug

Form Initial Hypothesis

Hypothesis: API endpoint is returning 500 error instead of 400

Evidence:
- Console shows "Network request failed"
- Server logs show 500 error at time of attempt
- Database logs show constraint violation

Next step: Check what's causing the 500

Phase 2: Pattern Analysis

Goal: Identify when bug occurs and when it doesn't

Questions to Answer:

When Does It Fail?
- Specific inputs?
- Certain users?
- Particular time of day?
- After specific sequence of actions?
When Does It Work?
- Any inputs that succeed?
- Any users unaffected?
- Worked before, broken now?

What Changed Recently?

# Check recent commits
git log --since="2 days ago" --oneline

# Check what changed in specific file
git log -p path/to/file.js

# See when bug was introduced
git bisect

Environmental Factors?
- Works locally, fails in production?
- Browser-specific?
- Network conditions?
- Load-related (works with 1 user, fails with 100)?

Pattern Analysis Example:

Bug Pattern Analysis:

FAILS when:
- Email contains + symbol (e.g., user+test@example.com)
- Password is exactly 8 characters
- User account was created after 2025-01-01

WORKS when:
- Email is standard format (user@example.com)
- Password is 9+ characters
- User account is older

Pattern identified: Email validation regex doesn't handle + symbol

Phase 3: Hypothesis Testing

Goal: Test theories systematically until root cause found

Process:

Create Minimal Test Case

// Isolate the bug
it('should accept email with plus symbol', () => {
  const email = 'user+test@example.com';
  const result = validateEmail(email);
  expect(result).toBe(true); // Currently fails
});

Add Instrumentation

function validateEmail(email) {
  console.log('Input email:', email);

  const regex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
  const isValid = regex.test(email);

  console.log('Regex test result:', isValid);
  console.log('Regex used:', regex);

  return isValid;
}

Test Hypothesis

// Hypothesis: Regex doesn't handle + symbol

// Test with minimal input
validateEmail('user+test@example.com');
// Output:
// Input email: user+test@example.com
// Regex test result: true
//
// Hypothesis REJECTED: Regex accepts + symbol

// Form new hypothesis: Something else is rejecting it

// Check database constraint
// Found: Database column has CHECK constraint excluding +
// Hypothesis CONFIRMED!

Iterate Until Root Cause Found Keep forming and testing hypotheses until you identify exact cause.

Phase 4: Implementation

Goal: Fix bug permanently with regression protection

Process:

Write Test Reproducing Bug

// This test should FAIL before fix
it('should accept email with plus symbol', async () => {
  const email = 'user+test@example.com';
  const password = 'SecureP@ss123';

  const response = await request(app)
    .post('/api/auth/register')
    .send({ email, password });

  expect(response.status).toBe(201);
  expect(response.body.user.email).toBe(email);
});

Run test - verify it fails:

npm test
# ✗ should accept email with plus symbol
#   Expected: 201, Received: 400

Fix the Bug

-- Remove overly restrictive database constraint
ALTER TABLE users DROP CONSTRAINT email_format_check;

-- Or update to correct constraint
ALTER TABLE users ADD CONSTRAINT email_format_check
  CHECK (email ~* '^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}$');

Verify Test Passes

npm test
# ✓ should accept email with plus symbol

Add Regression Tests

// Add more tests for similar edge cases
describe('email validation - special characters', () => {
  const validEmails = [
    'user+test@example.com',
    'user.name@example.com',
    'user_name@example.com',
    'user-name@example.com',
    'user123@example.com'
  ];

  validEmails.forEach(email => {
    it(`should accept ${email}`, async () => {
      const response = await request(app)
        .post('/api/auth/register')
        .send({ email, password: 'SecureP@ss123' });

      expect(response.status).toBe(201);
    });
  });
});

Document Root Cause

/*
 * Bug Fix: Email validation now accepts RFC-compliant characters
 *
 * Root Cause:
 * Database CHECK constraint was too restrictive, excluding the + symbol
 * which is valid in email addresses per RFC 5322.
 *
 * Fix:
 * Updated CHECK constraint to use proper regex pattern matching RFC 5322.
 *
 * Date: 2025-01-17
 * Related Issue: #234
 */

Commit Fix with Context

git add migrations/003_fix_email_constraint.sql
git add tests/auth/register.test.js
git commit -m "fix: Accept + symbol in email addresses

Database CHECK constraint was rejecting valid emails containing
the + symbol. Updated constraint to match RFC 5322 standard.

Closes #234"

Test Coverage Analysis

Goal: Identify untested code

Check Coverage:

# Generate coverage report
npm run test:coverage

# Typical output:
# File           | % Stmts | % Branch | % Funcs | % Lines |
# ---------------|---------|----------|---------|---------|
# src/auth.js    |   87.5  |    75.0  |  100.0  |   87.5  |
# src/orders.js  |   45.2  |    33.3  |   60.0  |   45.2  |

Identify Gaps:

Functions without any tests
Branches not covered (if statements, error paths)
Edge cases not tested
Integration paths missing

Prioritize:

Critical business logic (highest priority)
Security-sensitive code
Complex algorithms
Error handling paths
Edge cases

Best Practices

TDD Best Practices

Always write test first: No exceptions
One test at a time: Don't write multiple tests before implementing
Smallest possible step: Each cycle should be quick (5-10 minutes)
Test behavior, not implementation: Don't test private methods
Keep tests simple: Tests should be easier to understand than code

Test Quality

Clear test names: Should read like documentation
Arrange-Act-Assert: Structure tests consistently
One assertion per test: Makes failures clear
No logic in tests: Tests should be simple data
Independent tests: No test depends on another

Debugging Best Practices

Reproduce first: Can't fix what you can't reproduce
Understand before fixing: Don't guess and check
Fix root cause: Don't just treat symptoms
Add regression test: Prevent bug from returning
Document why: Help future debuggers

Integration with Superpowers

If superpowers:test-driven-development available:

Use for guided TDD workflow
Enhanced RED-GREEN-REFACTOR cycle
Additional TDD best practices

If superpowers:systematic-debugging available:

Use for complex debugging scenarios
Root cause tracing framework
Advanced instrumentation guidance

Common Anti-Patterns to Avoid

❌ Writing tests after implementation ❌ Changing tests to match implementation ❌ Testing implementation details instead of behavior ❌ Skipping refactor phase ❌ Testing code that's already tested (overwriting working tests) ❌ Making multiple changes before testing ❌ Debugging by randomly changing code ❌ Committing "console.log" debugging code

Notes

TDD is slower initially but faster overall (fewer bugs, less debugging)
Good tests are documentation that never gets outdated
Debugging is detective work, not guessing
Always add regression tests after fixing bugs
Test coverage is a minimum bar, not a goal

systematic-testing

Systematic Testing Skill

Purpose

Activation Triggers

Core Capabilities

1. Test-Driven Development (TDD)

2. Test Generation

Test Categories

Normal Cases (Happy Path)

Edge Cases (Boundary Conditions)

Error Cases (Invalid Inputs)

Integration Cases

Test Generation Template

3. Systematic Debugging Framework

Phase 1: Root Cause Investigation

Phase 2: Pattern Analysis

Phase 3: Hypothesis Testing

Phase 4: Implementation

Test Coverage Analysis

Best Practices

TDD Best Practices

Test Quality

Debugging Best Practices

Integration with Superpowers

Common Anti-Patterns to Avoid

Notes